The invention generally relates to roll cleaning apparatus for web or sheet production processes, and relates in particular, to roll cleaning apparatus for rolls in papermaking machines and web converting machines.
In a papermaking machine, web converting operation, or any other web or sheet production process it is often necessary to clean and/or condition the rotating roll surfaces or other moving surfaces that are used to convey the product. Inadequate cleaning of these moving surfaces will result in a build-up of contaminants and debris that may lead to product defects and production losses.
The contaminants that build up on these moving surfaces may include adhesive residue from use of recycled fiber, pitch, precipitated calcium carbonate (PCC), clay, starch or other polymers from coatings used in the product. Prior art cleaning systems generally utilized to remove contaminants on these moving surfaces include doctoring systems as well as abrasive pad type cleaning systems.
As shown in FIG. 1, certain doctor systems used for cleaning a roll generally employ a doctor blade 10 to scrape the moving surface of a roll 12. The doctor blade 10 is supported by a position adjustable doctor assembly 14 that may include a doctor blade holder 16 with a top plate 26, and unloading and loading tubes 18, 20 within a tube tray 22 that is mounted to a position adjustable doctor back 24. The loading and unloading tubes 18, 20 provide that the top plate 26 (as well as the doctor blade 10 attached thereto) are pivotally attached to the tube tray 22 via mounting structures 27, 28 and a rod 29 that joins the mounting structures 27, 28 together. The doctor back 24 is also adjustable to position the doctor assembly 16 toward and away from the roll 12.
Such doctor blades are generally effective in removing water, fiber build up and the product itself during threading or when a sheet break occurs. Doctor blades are also generally effective at removing contaminants of some appreciable thickness, which allows the working edge of the blade to get underneath and lift the contaminant away from the moving surface. Such doctor blades however, are typically not very effective at removing contaminants (or haze) that is of a very small particle size and may be in the microscopic grooves or pores of the roll surface. Additionally, doctor blades are not typically effective at removing contaminants of minimal thickness (<0.010 inches) that are adhered to the moving surface with a very high bond strength.
Other prior art cleaning systems include a device that applies an abrasive pad against a moving surface such as a roll surface. U.S. Pat. No. 5,597,449, for example, discloses a device for conditioning a surface 30 of a roll 32 wherein the device includes a grinding member 34 that is attached to a back-up part 36 as shown in FIG. 2. The back-up part 36 includes a groove 38 for receiving an elongated tip edge of a blade 40 to thereby form an articulation joint about which the back-up part 36 may pivot. The blade 40 is disclosed to be coupled to a doctor device. While such a device may be quickly placed on the tip of a doctor blade, it is questionable how well such a device would work for certain paper making applications. For example, and notwithstanding the disclosure in U.S. Pat. No. 5,597,449 of the use of an oscillation actuator, it is questionable how well such a device would work in applications that require significant applied forces and reciprocating forces given that the backing-part 36 rests against the tip edge of the blade 40 but is not attached to the blade 40. Moreover, any movement of the back-up part 36 with respect to the blade 40 would likely result in damage to the working edge of the blade 40.
Another prior art cleaning system disclosed in U.S. Pat. No. 5,597,449 includes a grinding member 42 that is attached to the working edge of a blade 44 adjacent the surface 30 of the roll 32 as shown in FIG. 3. The grinding material 42, however, is only attached to the end region of the blade 44 because only that region contacts the surface 30 of the roll 32. Moreover, the force of the grinding member 42 against the surface 30 is largely dependent on the stiffness of the blade 44, which will deflect when the applied force exceeds a certain threshold, thereby reducing an applied force against the surface 30.
Further prior art systems that include a cleaning pad provide improved cleaning, but further require substantially larger cleaning apparatus. For example, U.S. Pat. No. 7,465,374 discloses an apparatus for cleaning a roll in a papermaking machine, wherein a cleaning pad that conforms to the surface of a roll is mounted on a movable support structure that is movable into engagement with the roll surface. FIG. 4, for example, shows an embodiment that includes a scrubbing element 50 attached to a backing member 52, which in turn is attached to brackets 54 via fasteners 56. A longitudinal motion drive 58 is disclosed to be employed to move the brackets 54 via bearings 60 mounted on a block 62 in a reciprocal scrubbing motion. The drive 58 and block 62 are mounted on a movable plate 64 that is moveable with respect to a base plate 66 about a pin 68 via actuation of pneumatic bellows 70 such that the scrubbing element 50 is moved through a gap ‘G’ into and out of engagement with a surface of a roll 72. The position of the base plate 66 is bounded by a standoff 74 and a stop 76. Further devices disclosed in U.S. Pat. No. 7,465,374 include an internal plenum in the backing member 52 through which a vacuum is provided to draw particles from the surface of the roll 72 through grooves and openings in the backing member 52 adjacent the pad.
The above use of abrasive pads and positioning assemblies, however, require specialized equipment (including the base plate 66, the movable plate 64, the bellows 70 and the block 62), and the abrasive action is disclosed to be facilitated by the reciprocating (scrubbing) action that is provided by the longitudinal motion drive 58.
Although a doctor blade provides a low profile cleaning assembly, such a system is not effective for removing certain contaminants as discussed above, and although abrasive pad systems such as disclosed in U.S. Pat. No. 7,465,374 may provide improved cleaning in some applications, such cleaning apparatus are generally too large and costly for use in many applications. It is also desirable in some applications that a cleaning assembly be adapted to be readily, quickly and easily installed for application to a moving surface during machine down-time, yet also provide improved cleaning of the moving surface.
There remains a need therefore, for a cleaning system that can effectively remove various forms of contaminants from a moving surface (such as a roll or other moving surface) within a web or sheet processing system. Further, there remains a need for cleaning system that is compact so that it may be installed quickly and easily, without moving or modifying the doctor-back, for application to a moving surface during machine down-time, while also providing such improved performance removing various forms of contaminants from the moving surface.